Myeloid blood cell production initiating from hematopoietic stem and progenitor cells is regulated by a network of interacting accessory cell populations. Broxmeyer, H. E. and Williams, D. E., "The Production of Myeloid Blood Cells and Their Regulation During Health and Disease," CRC CRIT. REV. ONCOL./HEMATOL. 8:173 (1985). Accessory cells release biomolecules or cytokines which in turn can act either directly on hematopoietic stem and progenitor cells or indirectly through action on other accessory cells. Certain cytokines have already been implicated in the modulation of blood cell production. These include, but are not limited to, the hematopoietic colony stimulating factors (CSF): granulocyte-macrophage (GM)-CSF, macrophage (M)-CSF or CSF-1, granulocyte (G)-CSF, multi-CSF (also termed interleukin (IL)-3) and erythropoietin, as well as IL-1 through IL-6, the tumor necrosis factors-alpha and beta, the interferons,-alpha, beta and gamma, transforming growth factor-beta, E-type prostaglandins 1 and 2, lactoferrin, acidic isoferritin, activin and inhibin. Individual cytokines can act on more than one cell type and can have more than one effect. New cytokines continue to be described, and new functions are being attributed to them, as well as to previously described cytokines.